Thursday, February 7, 2008

Is It OK To Leave My Laptop Plugged In All the Time?

Reader Mike asks: Is it safe to leave my laptop plugged in for extended periods of time when I am not using it? I am talking 10 or 12 hours at a time. Or should I only plug it in when it needs charging?

There are actually two issues at play in this very common question: It it safe to leave a laptop plugged in all the time, and is it bad for the battery to do so? Let's look at both.

First, regarding safety, there's no evidence that shows that leaving your laptop plugged in will cause any sort of danger to the battery. You're right to worry, considering the battery explosions issue of 2006-07, but many of those laptops weren't plugged in at all when they went up in flames, and there's no evidence that those that were plugged in had been left that way for a long time, or that anything other than bad battery design was responsible for their failure.

The truth is that laptops and laptop batteries are designed with the intent that they be plugged in as often as possible. In fact, most manufacturers suggest leaving them plugged in all the time. The heat you feel from the bottom of a laptop that's been running all day doesn't really have anything to do with whether it's plugged in or not. Laptops get hot due to their internal components and the chemical reaction in the battery. The A/C charge has very little to do with it. So, from a pure safety standpoint: Plugged in is just fine.

The other question concerns your battery's lifespan. Will leaving it plugged in decrease its useful life? The short answer is no, at least not enough that you're likely to notice. Lithium-ion batteries have no "memory effect" like nickel-based batteries, so there's no worry about plugging them back in before they're completely drained. But like all batteries, lithium cells lose capacity over time. The more they are drained and recharged, the more their internal structure warps, and they eventually become unusable. This happens due to heat, and since your battery gets hot even when it isn't discharging, as long as you have it installed in a running computer, it's going to be affected to some extent. Now this effect is really pretty minimal compared to constant charge-discharge cycles, but if you turn off your laptop at night and unplug it, or if you run your laptop plugged in, without a battery installed, that battery will last slightly longer when you do eventually start using it (so long as you keep it properly charged most of the time). However, the extra lifespan you gain is not even remotely worth the extra hassle in doing all this work. Bottom line: Leave your notebook's battery installed, and plug it in as often as you can.